Tauopathy Mouse Research Articles

TREM2-Deficient Microglia Attenuate Tau Spreading In Vivo.

The role of TREM2 in Alzheimer's disease (AD) is not fully understood. Previous studies investigating the effect of TREM2 deletion on tauopathy mouse models without the contribution of b-amyloid have focused only on tau overexpression models. Herein, we investigated the effects of TREM2 deficiency on tau spreading using a mouse model in which endogenous tau is seeded to produce AD-like tau features. We found that Trem2-/- mice exhibit attenuated tau pathology in multiple brain regions concomitant with a decreased microglial density. The neuroinflammatory profile in TREM2-deficient mice did not induce an activated inflammatory response to tau pathology. These findings suggest that reduced TREM2 signaling may alter the response of microglia to pathological tau aggregates, impairing their activation and decreasing their capacity to contribute to tau spreading. However, caution should be exercised when targeting TREM2 as a therapeutic entry point for AD until its involvement in tau aggregation and propagation is better understood.

Altered transposable elements expression and gene networks remodeling precede disruptions in sleep/wake cycles in a tauopathy mouse model of AD

AbstractBackgroundAlzheimer’s Disease (AD) is an widespread neurodegenerative disorder, common in elder and Veterans communities, culminating in dementia with non‐cognitive behavioral and metabolic symptoms, such as hyperactivity and altered sleep/wake patterns. In demented patients, sleep/wake cycle disruptions facilitate weight loss, which is associated with adverse outcomes like accelerated AD progression and higher institutionalization. Tg4510 mice, which express a P301L mutant variant of human tau, develop both cognitive and non‐cognitive symptoms. Several mouse models of tau deposition, including Tg4510 mice, also have negative energy balance. To identify early factors affecting AD, we measured locomotor, sleep/wake patterns in vivo, and analyzed RNA‐seq data from Tg4510 mice to identify gene and transposable elements (TE) expression changes involved in behavioral derangements in AD.MethodLocomotor activity, sleep and wake intervals and patterns were measured using in vivo metabolic cages for two weeks over 24 hr and day and night cycles from Tg4510 mice (n = 5‐7) vs. controls (n = 7‐10) before and after the onset of tauopathy (at 2 and 7 months of age respectively). In additional experiments, we analyzed RNA‐seq from hippocampi of Tg4510 mice (n = 5) vs. controls (n = 6). Using our established TTESA bioinformatics pipeline, reads were aligned to reference genome and expression of genes or TEs was measured with featureCounts. Pathway enrichment analysis using Visual Annotation Display was used to discover common functional and disease pathways using Gene Ontology, Protein Ontology, and Mammalian Phenotype Ontology.ResultWe observed altered locomotor and sleep patterns during the night phase starting in young Tg4510 vs. controls. TTESA results detected the majority of significantly differentially expressed TEs were retrotransposons (70%), which consisted mainly of long terminal repeats (LTRs; 70%) and some LINE retroelements (30%) and SINEs (<8%) in transgenic mice. VLaD pathway analysis revealed several biological processes upregulated in transgenic mice, including non‐cognitive behavioral pathways were downregulated, such as the regulation of circadian sleep/wake cycle with changes in the expression levels of Per2, Per3 (p<0.0001).ConclusionEarly dysregulation of TEs may be involved in rewiring gene expression networks underlying behavioral changes in wake and sleep cycles and other circadian patterns of behavior in this humanized mouse model of AD.

Endogenous pathology in tauopathy mice progresses via brain networks

Endogenous pathology in tauopathy mice progresses via brain networks

Organotypic Hippocampal Slice Cultures from Adult Tauopathy Mice and Theragnostic Evaluation of Nanomaterial Phospho-TAU Antibody-Conjugates.

Organotypic slice culture models surpass conventional in vitro methods in many aspects. They retain all tissue-resident cell types and tissue hierarchy. For studying multifactorial neurodegenerative diseases such as tauopathies, it is crucial to maintain cellular crosstalk in an accessible model system. Organotypic slice cultures from postnatal tissue are an established research tool, but adult tissue-originating systems are missing, yet necessary, as young tissue-originating systems cannot fully model adult or senescent brains. To establish an adult-originating slice culture system for tauopathy studies, we made hippocampal slice cultures from transgenic 5-month-old hTau.P301S mice. In addition to the comprehensive characterization, we set out to test a novel antibody for hyperphosphorylated TAU (pTAU, B6), with and without a nanomaterial conjugate. Adult hippocampal slices retained intact hippocampal layers, astrocytes, and functional microglia during culturing. The P301S-slice neurons expressed pTAU throughout the granular cell layer and secreted pTAU to the culture medium, whereas the wildtype slices did not. Additionally, cytotoxicity and inflammation-related determinants were increased in the P301S slices. Using fluorescence microscopy, we showed target engagement of the B6 antibody to pTAU-expressing neurons and a subtle but consistent decrease in intracellular pTAU with the B6 treatment. Collectively, this tauopathy slice culture model enables measuring the extracellular and intracellular effects of different mechanistic or therapeutic manipulations on TAU pathology in adult tissue without the hindrance of the blood-brain barrier.

Visual Evoked Potentials as an Early-Stage Biomarker in the rTg4510 Tauopathy Mouse Model.

Tauopathies such as Alzheimer's disease (AD) and frontotemporal dementia (FTD) are characterized by formation of neurofibrillary tangles consisting of hyperphosphorylated tau protein. Early pathophysiological and functional changes related to neurofibrillary tangles formation are considered to occur prior to extensive neurodegeneration. Hyperphosphorylated tau has been detected in postmortem retinas of AD and FTD patients, and the visual pathway is an easily accessible system in a clinical setting. Hence, assessment of the visual function may offer the potential to detect consequences of early tau pathology in patients. The aim of this study was to evaluate visual function in a tauopathy mouse model in relation to tau hyperphosphorylation and neurodegeneration. In this study we explored the association between the visual system and functional consequences of tau pathology progression using a tauopathy rTg4510 mouse model. To this end, we recorded full-field electroretinography and visual evoked potentials in anesthetized and awake states at different ages. While retinal function remained mostly intact within all the age groups investigated, we detected significant changes in amplitudes of visual evoked potential responses in young rTg4510 mice exhibiting early tau pathology prior to neurodegeneration. These functional alterations in the visual cortex were positively correlated with pathological tau levels. Our findings suggest that visual processing could be useful as a novel electrophysiological biomarker for early stages of tauopathy.

The Effects of a Blood-Brain Barrier Penetrating Erythropoietin in a Mouse Model of Tauopathy.

Erythropoietin (EPO), a hematopoietic neurotrophin, is a potential therapeutic for Alzheimer's disease (AD) but has limited blood-brain barrier (BBB) permeability. EPO fused to a chimeric transferrin receptor monoclonal antibody (cTfRMAb) enters the brain via TfR-mediated transcytosis across the BBB. We previously showed that cTfRMAb-EPO is protective in a mouse model of amyloidosis, but its effects on tauopathy are not known. Given that amyloid and tau pathology are characteristics of AD, the effects of cTfRMAb-EPO were studied in a tauopathy mouse model (PS19). Six-month-old PS19 mice were injected intraperitoneally with either saline (PS19-Saline; n = 9) or cTfRMAb-EPO (PS19-cTfRMAb-EPO, 10 mg/kg; n = 10); every two or three days on alternate weeks for 8 weeks. Age-matched, saline-treated, wildtype littermates (WT-Saline; n = 12) were injected using the same protocol. After 8 weeks, locomotion, hyperactivity, and anxiety were assessed via the open-field test, and brains were harvested and sectioned. Cerebral cortex, hippocampus, amygdala, and entorhinal cortex sections were analyzed for phospho-tau (AT8) and microgliosis (Iba1). Hippocampal cellular density (H&E) was also assessed. PS19-Saline mice were hyperactive and less anxious compared to WT-Saline mice, and these behavioral phenotypes were significantly reduced in the PS19-cTfRMAb-EPO mice compared to the PS19-Saline mice. cTfRMAb-EPO significantly reduced AT8 load by ≥50% in all of the brain regions analyzed and microgliosis in the entorhinal cortex and amygdala compared to the PS19-Saline mice. Hippocampal pyramidal and granule cell layer density did not differ significantly between the PS19-cTfRMAb-EPO and PS19-Saline mice. This proof-of-concept study demonstrates the therapeutic effects of the BBB-penetrating cTfRMAb-EPO in PS19 mice.

Activation of TRPV4 induces intraneuronal tau hyperphosphorylation via cholesterol accumulation

Transient receptor potential vanilloid 4 (TRPV4) is a non-selective cation channel, whose aberrant function in neurons has been reported to participate in the progression of brain disorders, including Alzheimer's disease (AD). However, the influence of TRPV4 activation on tau hyperphosphorylation in AD has not yet been elucidated. Since disturbed brain cholesterol homeostasis is considered to be related to excessive tau phosphorylation, this study aimed to explore whether dysregulation of TRPV4 affects tau phosphorylation and whether it involves cholesterol unbalance. Our data indicated that TRPV4 activation increased tau phosphorylation in the cortex and hippocampus of P301S tauopathy mouse model and aggravated its cognitive decline. In addition, we detected that TRPV4 activation upregulated cholesterol levels in primary neurons, and the elevation of cholesterol promoted hyperphosphorylation of tau. TRPV4 knockdown improved tau hyperphosphorylation by reducing intracellular cholesterol accumulation. Our results suggest that activation of TRPV4 may take part in the pathological mechanism of AD by promoting intraneuronal tau hyperphosphorylation in a cholesterol-dependent manner.

Selective dysfunction of fast-spiking inhibitory interneurons and disruption of perineuronal nets in a tauopathy mouse model

In Alzheimer's disease (AD), network hyperexcitability is frequently observed and associated with subsequent cognitive impairment. Dysfunction of inhibitory interneurons (INs) is thought to be one of the key biological mechanisms of hyperexcitability. However, it is still unknown how INs are functionally affected in tau pathology, which is a major pathology in AD. To clarify this, we evaluated the neuronal activity of cortical INs in 6-month-old rTg4510 mice, a model of tauopathy. Calcium imaging with mDlx enhancer-driven labeling revealed that neuronal activity in INs was decreased in rTg4510 mice. In the patch clamp recording, the firing properties of fast-spiking INs were altered so as to reduce their activity in rTg4510 mice. In parallel with microglial activation, perineuronal nets around parvalbumin-positive INs were partially disrupted in rTg4510 mice. Taken together, our data indicate that the excitability of cortical fast-spiking INs is decreased, possibly because of the disruption of perineuronal nets.

Neuronal APOE4 removal protects against tau-mediated gliosis, neurodegeneration and myelin deficits

Apolipoprotein E4 (APOE4) is the strongest known genetic risk factor for late-onset Alzheimer’s disease (AD). Conditions of stress or injury induce APOE expression within neurons, but the role of neuronal APOE4 in AD pathogenesis is still unclear. Here we report the characterization of neuronal APOE4 effects on AD-related pathologies in an APOE4-expressing tauopathy mouse model. The selective genetic removal of APOE4 from neurons led to a significant reduction in tau pathology, gliosis, neurodegeneration, neuronal hyperexcitability and myelin deficits. Single-nucleus RNA-sequencing revealed that the removal of neuronal APOE4 greatly diminished neurodegenerative disease-associated subpopulations of neurons, oligodendrocytes, astrocytes and microglia whose accumulation correlated to the severity of tau pathology, neurodegeneration and myelin deficits. Thus, neuronal APOE4 plays a central role in promoting the development of major AD pathologies and its removal can mitigate the progressive cellular and tissue alterations occurring in this model of APOE4-driven tauopathy.

Focused Ultrasound-mediated Liquid Biopsy in a Tauopathy Mouse Model.

Background Neurodegenerative disorders (such as Alzheimer disease) characterized by the deposition of various pathogenic forms of tau protein in the brain are collectively referred to as tauopathies. Identification of the molecular drivers and pathways of neurodegeneration is critical to individualized targeted treatment of these disorders. However, despite important advances in fluid biomarker detection, characterization of these molecular subtypes is limited by the blood-brain barrier. Purpose To evaluate the feasibility and safety of focused ultrasound-mediated liquid biopsy (sonobiopsy) in the detection of brain-derived protein biomarkers in a transgenic mouse model of tauopathy (PS19 mice). Materials and Methods Sonobiopsy was performed by sonicating the cerebral hemisphere in 2-month-old PS19 and wild-type mice, followed by measurement of plasma phosphorylated tau (p-tau) species (30 minutes after sonication in the sonobiopsy group). Next, spatially targeted sonobiopsy was performed by sonicating either the cerebral cortex or the hippocampus in 6-month-old PS19 mice. To detect changes in plasma neurofilament light chain (a biomarker of neurodegeneration) levels, blood samples were collected before and after sonication (15 and 45-60 minutes after sonication). Histologic staining was performed to evaluate tissue damage after sonobiopsy. The Shapiro-Wilk test, unpaired and paired t tests, and the Mann-Whitney U test were used. Results In the 2-month-old mice, sonobiopsy significantly increased the normalized levels of plasma p-tau species compared with the conventional blood-based liquid biopsy (p-tau-181-to-mouse tau [m-tau] ratio: 1.7-fold increase, P = .006; p-tau-231-to-m-tau ratio: 1.4-fold increase, P = .048). In the 6-month-old PS19 mice, spatially targeted sonobiopsy resulted in a 2.3-fold increase in plasma neurofilament light chain after sonication of the hippocampus and cerebral cortex (P < .001). After optimization of the sonobiopsy parameters, no excess microhemorrhage was observed in the treated cerebral hemisphere compared with the contralateral side. Conclusion This study showed the feasibility of sonobiopsy to release phosphorylated tau species and neurofilament light chain to the blood circulation, potentially facilitating diagnosis of neurodegenerative disorders. © RSNA, 2023 Supplemental material is available for this article. See also the editorial by Fowlkes in this issue.

Early impairments of visually-driven neuronal ensemble dynamics in the rTg4510 tauopathy mouse model

Tau protein pathology is a hallmark of many neurodegenerative diseases, including Alzheimer's Disease or frontotemporal dementia. Synaptic dysfunction and abnormal visual evoked potentials have been reported in murine models of tauopathy, but little is known about the state of the network activity on a single neuronal level prior to brain atrophy. In the present study, oscillatory rhythms and single-cell calcium activity of primary visual cortex pyramidal neuron population were investigated in basal and light evoked states in the rTg4510 tauopathy mouse model prior to neurodegeneration. We found a decrease in their responsivity and overall activity which was insensitive to GABAergic modulation. Despite an enhancement of basal state coactivation of cortical pyramidal neurons, a loss of input-output synchronicity was observed. Dysfunction of cortical pyramidal function was also reflected in a reduction of basal theta oscillations and enhanced susceptibility to a sub-convulsive dose of pentylenetetrazol in rTg4510 mice. Our results unveil impairments in visual cortical pyramidal neuron processing and define aberrant oscillations as biomarker candidates in early stages of neurodegenerative tauopathies.

CSF1R inhibitors induce a sex-specific resilient microglial phenotype and functional rescue in a tauopathy mouse model

Microglia are central to pathogenesis in many neurological conditions. Drugs targeting colony-stimulating factor-1 receptor (CSF1R) to block microglial proliferation in preclinical disease models have shown mixed outcomes, thus the therapeutic potential of this approach remains unclear. Here, we show that CSF1R inhibitors given by multiple dosing paradigms in the Tg2541 tauopathy mouse model cause a sex-independent reduction in pathogenic tau and reversion of non-microglial gene expression patterns toward a normal wild type signature. Despite greater drug exposure in male mice, only female mice have functional rescue and extended survival. A dose-dependent upregulation of immediate early genes and neurotransmitter dysregulation are observed in the brains of male mice only, indicating that excitotoxicity may preclude functional benefits. Drug-resilient microglia in male mice exhibit morphological and gene expression patterns consistent with increased neuroinflammatory signaling, suggesting a mechanistic basis for sex-specific excitotoxicity. Complete microglial ablation is neither required nor desirable for neuroprotection and therapeutics targeting microglia must consider sex-dependent effects.

Evolutionarily conserved regulators of tau identify targets for new therapies

Tauopathies are neurodegenerative diseases that involve the pathological accumulation of tau proteins; in this family are Alzheimer disease, corticobasal degeneration, and chronic traumatic encephalopathy, among others. Hypothesizing that reducing this accumulation could mitigate pathogenesis, we performed a cross-species genetic screen targeting 6,600 potentially druggable genes in human cells and Drosophila. We found and validated 83 hits in cells and further validated 11 hits in the mouse brain. Three of these hits (USP7, RNF130, and RNF149) converge on the C terminus of Hsc70-interacting protein (CHIP) to regulate tau levels, highlighting the role of CHIP in maintaining tau proteostasis in the brain. Knockdown of each of these three genes in adult tauopathy mice reduced tau levels and rescued the disease phenotypes. This study thus identifies several points of intervention to reduce tau levels and demonstrates that reduction of tau levels via regulation of this pathway is a viable therapeutic strategy for Alzheimer disease and other tauopathies.

Inhibition of histone methyltransferase Smyd3 rescues NMDAR and cognitive deficits in a tauopathy mouse model

Pleiotropic mechanisms have been implicated in Alzheimer’s disease (AD), including transcriptional dysregulation, protein misprocessing and synaptic dysfunction, but how they are mechanistically linked to induce cognitive deficits in AD is unclear. Here we find that the histone methyltransferase Smyd3, which catalyzes histone H3 lysine 4 trimethylation (H3K4me3) to activate gene transcription, is significantly elevated in prefrontal cortex (PFC) of AD patients and P301S Tau mice, a model of tauopathies. A short treatment with the Smyd3 inhibitor, BCI-121, rescues cognitive behavioral deficits, and restores synaptic NMDAR function and expression in PFC pyramidal neurons of P301S Tau mice. Fbxo2, which encodes an E3 ubiquitin ligase controlling the degradation of NMDAR subunits, is identified as a downstream target of Smyd3. Smyd3-induced upregulation of Fbxo2 in P301S Tau mice is linked to the increased NR1 ubiquitination. Fbxo2 knockdown in PFC leads to the recovery of NMDAR function and cognitive behaviors in P301S Tau mice. These data suggest an integrated mechanism and potential therapeutic strategy for AD.

New unexpected role for Wolfram Syndrome protein WFS1: a novel therapeutic target for Alzheimer's disease?

New unexpected role for Wolfram Syndrome protein WFS1: a novel therapeutic target for Alzheimer's disease?

Lowering Synaptogyrin‐3 Expression Rescues Tau‐Induced Memory Deficits and Synaptic Loss in the Presence of Microglial Activation

AbstractBackgroundTau is implicated in multiple neurodegenerative disorders, including Alzheimer’s disease. Synaptic loss and neuroinflammation are characteristic feautures of tauopathies, but it is unclear if these pathological events are causally linked and whether they are relevant for cognitive decline. Mutations and/or hyperphosphorylation of Tau leads its accumulation at synapses, where Tau binds to synaptic vesicle‐associated protein Synaptogyrin‐3 resulting in clustering of vesicles and impaired synaptic function. Given that Synaptogyrin‐3 is uniquely present at pre‐synaptic terminals, this allows us to decipher the contribution of pre‐synaptic Tau to overall Tau‐induced pathology.MethodWe generated a synaptogyrin‐3 knockout mouse line using CRISPR‐Cas9 technology. Synaptogyrin‐3−/− and +/− mice are viable and fertile and do not show overt phenotypes. We bred synaptogyrin‐3+/− mice with human Tau P301S‐expressing mice (PS19 line) and aged the offspring. We used several techniques, including electrophysiology, behavioral tests, immunohistochemistry and electron microscopy, to determine the effects of lowering Synaptogyrin‐3 expression in a tauopathy mouse model.ResultWe found that heterozygous knockout of Synaptogyrin‐3 in Tau P301S mice was sufficient to rescue synaptic plasticity and working memory defects. Moreover, lowering Synaptogyrin‐3 expression prevented synaptic degeneration and loss of synaptic markers in Tau P301S mice. Interestingly, proliferation and activation of astrocytes and microglia are observed in Tau P301S; synaptogyrin‐3+/− mice to the same extent as in their Tau P301S littermates.ConclusionOur results indicate that Tau induces synaptic loss and neuroinflammation independently, and that neuroinflammation is not sufficient to cause synaptic loss. In addition, pre‐synaptic defects caused by Tau are enough to drive defects in working memory.

Neuronal calcium dysregulation in mice at an early stage of tauopathy and its alleviation by a tau antibody

AbstractBackgroundTau immunotherapies are promising approaches to treat Alzheimer’s disease and other tauopathies. How tau antibodies restore neuronal function remains unknown. Neuronal activity can be monitored by two‐photon calcium imaging in awake and behaving animals. Using this method, we observed altered neuronal calcium activity in the motor cortex of 12‐month‐old JNPL3 tauopathy mice during quiet wakefulness or forced running (Wu Q et al, Neurobiol. Dis. 2021). We also demonstrated that a mouse monoclonal antibody, targeting phosphorylated tau‐Ser396/Ser404, significantly restored the abnormal calcium activity and decreased pathological tau levels in these mice. Analysis of possible neuronal functional deficits and tau antibody efficacy in younger tauopathy mice warrants further investigation.MethodsSomatic calcium activity in the motor cortex of 6‐month‐old JNPL3 mice were assessed by two‐photon microscopy when animals were either resting or running on a treadmill. At this age, JNPL3 mice are in their early stage of tauopathy. The frequency, amplitude and total activity of calcium transients were analyzed and compared between wild‐type and JNPL3 mice. After the first imaging session, two doses (100 µg each) of a tau antibody were administered intravenously to JNPL3 mice four days apart. The somatic calcium activity was assessed again in these animals four days later, and compared to their neuronal calcium activity profile before tau antibody treatment.ResultsWe found abnormal cortical calcium activity in resting and running JNPL3 mice at 6 months of age. Brain levels of pathological tau correlated with the degree of calcium dysfunction. Acute treatment with a tau antibody attenuated these changes, whereas littermate JNPL3 mice treated with control IgG showed no improvements.ConclusionThese findings revealed neuronal calcium dysregulation in JNPL3 mice at an early stage of tauopathy that was partially corrected by an acute tau antibody treatment, analogous to our prior findings at a later stage of tauopathy. Together, these results indicate that neuronal dysfunction correlates with tau pathology at various stages of tauopathy, which can be consistently alleviated by a tau antibody treatment. This type of functional evaluation in vivo is a valuable way to study tau pathogenesis, and assess therapeutic efficacy at different stages of tauopathy.

The systemic disruption of P2rx7 alleviates tau pathology in P301S tau mice via inhibition of extracellular vesicle release

AbstractBackgroundP2X purinoceptor 7 (P2RX7), an ATP‐gated cation channel present abundantly in the microglia, induces membrane depolarization and extracellular vesicle (EV) secretion. Previous study demonstrated that administration of GSK1482160, a P2RX7 selective inhibitor, suppressed EVs secretion from murine microglia resulting in accumulation of Tsg101+ intraluminal vesicles (ILVs) in the hippocampus, and restored partial behavioral deficits in P301S tau mice. However, the specificity of GSK1482160 to P2RX7 has never been investigated in P301S tau mice. It is crucial to validate whether P2RX7 is a potential target for alleviating the tauopathy phenotype in P301S tau mice. The purpose of this study is to determine if deletion of P2RX7 is sufficient to recapiturate the therapeutic effect of GSK1482160 in tauopathy mouse model.MethodFours and nine‐months‐old P2RX7‐/‐:P301S and P301S mice were generated for the evaluation of ILV accumulation and tau pathology. Primary microglia and astrocytes from WT (C57BL/6) and P2RX7‐/‐ mice, treated with GSK1482160 and ATP for EV secretion. EVs were isolated from conditioned media via the sequential centrifugation and ultracentrifugation. Finally, EVs were quantified by nanoparticle tracking analysis and exosome specific marker CD9 ELISA. Effects of GSK1482160 on EVs secretion from astrocytes/microglia were also assessed using Western blot with EV specific markers Tsg101 and CD9.ResultExosome specific marker Tsg101, CD9, and tau expression levels were reduced in the hippocampus of nine‐months‐old P2RX7‐/‐:P301S mice compared to P301S mice. No significant difference between the two groups at 4 months of age was observed. Strikingly, primary cultured microglia and astrocytes showed reduction in EV secretion in both ATP stimulated or unstimulated condition from P2RX7‐/‐ group compared to WT group. Additionally, GSK1482160 pretreatment significantly reduced EV secretion from WT astrocytes and microglia, although it had no effects in P2RX7‐/‐ cells. These findings were validated by ELISA of EV marker CD9 and immunoblotting of Tsg101 and flotillin‐1 using isolated EVs.ConclusionResults demonstrate that P2RX7 is primarily responsible for ATP‐induced EV secretion from astrocytes and microglia, and systemic disruption of P2RX7 mimics the effect of GSK1482160 in P301S tau mice, including accumulation of ILVs in microglia and suppression of tau accumulation in the hippocampal regions.

Brain Derived Biologically Relevant Tau Oligomers

AbstractBackgroundNeurodegenerative Tauopathies, including Alzheimer’s disease (AD), are characterized by the appearance of extracellular lesions composed of aggregated and post‐translationally modified tau proteins. The resulting tau pathology is an established marker for differential disease diagnosis and staging, a surrogate marker for neurodegeneration, a potential vector for disease propagation, and a source of toxicity in biological models. In comparison to the well‐established methods for isolation/preparation and biochemical and structural characterization of stable tau filaments from tauopathy brain, the characterization of smaller and much dynamic oligomeric tau aggregates has not been investigated to the same degree. As a result, tau oligomers that may associate most closely with disease propagation and toxicity as suggested by a large body of research, are not fully established.MethodHerein, we leverage our well‐optimized brain‐derived tau oligomers (BDTOs) from well‐vetted human tauopathy cases of AD, progressive supranuclear palsy (PSP) and dementia with Lewy bodies (DLB). In addition to our rigorous biochemical characterization of the BDTOs by immunological probing, and structural characterization by proteolysis and microscopic analyses, we have optimized Fluorescent Amyloid Multi Emission Spectra (FLAMES) microscopy for cataloging and comparing tau conformational variants across a wide range of samples, from brain tissue sections and BDTOs to in vitro aggregated tau assemblies. For selective immunodetection of the BDTOs, we have used our novel four fully sequenced and epitope mapped Tau Oligomer Monoclonal Antibodies (TOMAs), which recognize non‐continuous sequences on tau. Furthermore, the bioactivity of the BDTOs was assessed by evaluating their seeding propensity in biosensor cells and primary cortical neurons from tauopathy mice and their effects on synaptic function by electrophysiological studies.ResultWe observed that the BDTOs differed in their immunological properties, morphology, and sensibility/stability to proteolysis. The BDTOs were distinguished based on FLAMES spectral signature. Distinct seeding propensity and impairment of long‐term potentiation (LTP) indicated their differences in bioactivity as well.ConclusionOur thorough investigation/characterization of biologically active disease‐relevant tau oligomers will provide new opportunities to diagnose and evaluate therapeutics beyond the current capabilities for AD and related tauopathies by developing specific tau aggregation inhibitors and/or diagnostic probes for pathological tau protein.

P75NTR modulation counteracts alterations in neuronal and glial activity‐dependent profiles of gene co‐expression networks in tauopathy mice

AbstractBackgroundP75NTR is a key mediator in the regulation of neuronal plasticity, and modulation of its signaling prevents synaptic dysfunction in Tau.P301S mice, as measured by long‐term potentiation (LTP). Since LTP alters gene expression programs and results in transient post‐translational modifications at synapses, we asked whether tauopathy‐associated alterations in gene co‐expression, in response to stimulation, can be counteracted by p75NTR modulation. MethodLM11A‐31 (C31), a small molecule p75NTR modulator, was orally administered to Wildtype (WT) and Tau.P301S mice for 3 months, at a time when tau pathology was fully developed. RNA sequencing with cell‐type enrichment analysis was performed on unstimulated and stimulated hippocampal slices that underwent theta burst stimulation (TBS) to induce late‐phase LTP and generate activity‐dependent profiles of gene co‐expression networks, using weighted analysis with a soft‐threshold power of 18 to achieve scale‐free topology R2&gt;0.8 and module size 25.ResultThe most significantly expressed activity‐dependent transcriptional co‐expression modules related to synaptic function in WT mice, that were down‐regulated in Tau.P301S mice, showed an enrichment for genes in neurons and transcripts selectively expressed in CA1 pyramidal cells. The top significant gene pathways enriched in these modules were glutamatergic synapse, post‐synapse, pre‐synapse, post‐synaptic density, dendritic and neuron spine, with Cacna1h, Gabbr1, Kalrn, Shisa7, and Epha7. All of these were normalized to WT levels with C31 treatment. In addition, significantly up‐regulated co‐expression modules in Tau.P301S relative to WT mice associated with pathways such as complement binding, immune system process, myeloid leukocyte migration and neutrophil chemotaxis were enriched in genes found in microglia, such as Trem2, C1qa, C1qb, C1qc, Tyrobp. Notably, these expression profiles also reverted to WT levels with C31. Further, comparison of mouse and human modules demonstrated that those affected in treated mice have similar up‐ and down‐regulated patterns of expression as those found in human AD.ConclusionModulation of p75NTR with C31 normalized tauopathy‐related neuronal and glial transcriptional profiles. These transcriptional alterations are in part concordant with alterations found in human AD‐relevant gene co‐expression networks.